Systems and methods for customizing interactive virtual boundaries

ABSTRACT

A method for customizing an interactive boundary based on a patient-specific feature, includes displaying a graphical representation of an implant in virtual coordinate space and displaying a graphical representation of a bone in virtual coordinate space. The method further includes positioning the graphical representation of the implant relative to the graphical representation of the bone based on a user input and extracting reference feature information associated with the virtual representation of the implant. The method further includes mapping the extracted reference feature information to the graphical representation of the bone, receiving information indicative of a positional landmark associated with the bone, and estimating an intersection between the positional landmark and the mapped reference feature. A virtual boundary is generated based, at least in part, on the estimated intersection between the positional landmark and the mapped reference feature.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/725,513, filed Dec. 21, 2012, which claims the benefit of andpriority to U.S. Provisional Application No. 61/581,632, filed Dec. 30,2011, both of which are hereby incorporated by reference herein in theirentireties.

BACKGROUND

The present disclosure relates generally to force feedback systemsassociated with computer-assisted surgery (“CAS”) systems and, moreparticularly, to systems and methods for customizing interactive hapticboundaries associated with CAS systems based on patient-specificinformation.

The knee joint comprises the interface between the distal end of thefemur and the proximal end of the tibia. In a properly-functioning kneejoint, medial and lateral condyles of the femur pivot smoothly alongmenisci attached to respective medial and lateral condyles of the tibia.When the knee joint is damaged, the natural bones and cartilage thatform the joint may be unable to properly articulate, which can lead tojoint pain and, in some cases, interfere with normal use of the joint.

In some situations, surgery is required to restore normal use of thejoint and reduce pain. Depending upon the severity of the damage, thesurgery may involve partially or completely replacing the joint withprosthetic components. During such knee replacement procedures, asurgeon resects damaged portions of the bone and cartilage, whileattempting to leave healthy tissue intact. The surgeon then fits thehealthy tissue with artificial prosthetic components designed toreplicate the resected tissue and restore proper knee joint operation.

Typically, prior to the surgery, the surgeon develops a preliminary(“pre-operative”) plan that serves as a guide to performing the surgery.As part of the pre-operative planning, the surgeon surveys, among otherthings, the size, shape, kinematic function, and condition of thepatient's joint. Using computer-assisted surgery systems, this surveycan be performed by obtaining computer-based images of the joint andgenerating a computer-based model of the joint of the patient in virtualsoftware space. Using this virtual model, the surgeon can evaluate thecondition of the anatomical features of the joint and plan, among otherthings, the location and amount of bone that needs to be removed and theposition and orientation in which the prosthetic components should beimplanted on the bone to restore normal joint functionality.

Although the surgeon has a great degree of flexibility in customizingmost aspects of the surgery based on the unique anatomy of the patient,the surgeon is typically limited to selecting from among a fairly smallnumber of different prosthetic implant components. In many situations, asurgeon performs surgery on a patient whose anatomy does not preciselymatch any of the available prosthetic implant components. As a result,the surgeon may be required to select the prosthetic implant that mostclosely fits—but does not precisely match—the patient's anatomy. Thesurgeon can then modify the surgical plan (either pre orintra-operatively) to accommodate for the selected prostheticcomponents.

In some situations, the CAS system may include a force feedback controlsystem that is coupled to one or more surgical instruments (e.g.,cutting tools) and configured to provide force feedback for controllingthe surgical instrument during the surgery. The force feedback controlsystem may constrain the cutting tool to limit the position or operationof the surgical instrument to within certain predefined boundaries. Byallowing users to strategically define the placement of the virtualboundaries associated with the force feedback control system, these CASsystems enable surgeons to precisely and accurately control theresection and sculpting of the bone in preparation for receiving theprosthetic implant.

Because CAS systems provide a solution for accurately, reliably, andprecisely executing bone cuts by defining the boundaries at which acutting surface of a surgical instrument can operate, some CAS systemsnow include virtual software models that match the size and shape ofavailable prosthetic implants. The virtual software model of theimplant(s) can be positioned (in software) relative to the virtualmodel(s) of the patient's joint prior to or during the surgicalprocedure. Once positioned, the software model of the implant may be“registered” to the virtual model of the patient's anatomy so that thecutting surface is constrained to operate only within the area definedby the software model of the implant, limiting tissue removal only tothe specific area of the patient's bone associated with the registeredplacement of the implant.

Although systems that provide virtual models (and corresponding hapticboundaries) associated with a selection of available implants allowsurgeons to quickly and efficiently define a resection pattern forpreparing the bone to receive the implant, they may nonetheless havelimitations that make them less than optimal. Specifically, each virtualimplant model is associated with a corresponding fixed haptic boundary,which may be limited in size and shape to the geometry associated withthe virtual implant model. This may be particularly problematic insituations in which the surgeon is forced to select an undersizedprosthetic implant, but nonetheless wishes to remove areas of diseasedor damaged tissue that may be located beyond the boundaries required toaccommodate the undersized prosthetic implant.

The presently disclosed systems and methods for customizing interactivehaptic boundaries are directed to overcoming one or more of the problemsset forth above and/or other problems in the art.

SUMMARY

In accordance with one aspect, the present disclosure is directed to amethod for customizing an interactive haptic boundary based on apatient-specific feature. The method may comprise identifying areference feature associated with a virtual implant model. The methodmay also comprise determining an intersection between the identifiedreference feature and a virtual model associated with an anatomy of thepatient. A virtual haptic boundary may be generated based on thedetermined intersection between the identified reference featureassociated with the virtual implant model and the virtual modelassociated with the anatomy of the patient.

According to another aspect, the present disclosure is directed toanother method for customizing an interactive haptic boundary based on apatient-specific feature. The method may comprise displaying a graphicalrepresentation of an implant in virtual coordinate space and displayinga graphical representation of a bone in virtual coordinate space. Themethod may further comprise positioning the graphical representation ofthe implant relative to the graphical representation of the bone basedon a user input. The method may also comprise extracting referencefeature information associated with the virtual representation of theimplant, and mapping the extracted reference feature information to thegraphical representation of the bone. Information indicative of apositional landmark associated with the bone may be received. Anintersection between the positional landmark and the mapped referencefeature may be estimated, and a virtual haptic boundary may be generatedbased, at least in part, on the estimated intersection between thepositional landmark and the mapped reference feature.

In accordance with yet another aspect, the present disclosure isdirected to a computer-assisted surgery system comprising a display, aninput device configured to receive data input by a user, and aprocessor, operatively coupled to the input device and the display. Theprocessor may be configured to identify a reference feature associatedwith a virtual implant model, and determine an intersection between theidentified reference feature and a virtual model associated with ananatomy of the patient. The processor may also be configured to generatea virtual haptic boundary based on the determined intersection betweenthe identified reference feature associated with the virtual implantmodel and the virtual model associated with the anatomy of the patient.The processor may also be configured to display the generated virtualhaptic boundary and the virtual model associated with the anatomy of thepatient on the display.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention will be realized and attained bymeans of the elements and combinations particularly pointed out in theappended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments that,together with the description, serve to explain the principles andfeatures of the present disclosure.

FIG. 1 illustrates a perspective view of post-operative prosthetic kneejoint fitted with a cruciate-retaining prosthetic system, consistentwith certain disclosed embodiments;

FIG. 2 provides a schematic illustration of an exemplarycomputer-assisted surgery (CAS) system, in which certain methodsconsistent with the disclosed embodiments may be implemented;

FIG. 3 provides a schematic diagram of an exemplary computer system,which may be used in one or more components associated with the CASsystem illustrated in FIG. 2;

FIG. 4 illustrates an exemplary screen shot associated with a graphicaluser interface of the CAS system, in accordance with certain disclosedembodiments;

FIG. 5 illustrates another exemplary screen shot associated with agraphical user interface of CAS system, in accordance with the disclosedembodiments;

FIG. 6 provides a flowchart illustrating an exemplary method forgenerating interactive haptic boundaries based on patient-specificanatomic data;

FIG. 7 provides a flowchart illustrating an exemplary method formodifying an interactive haptic boundary based on patient-specificanatomic data; and

FIG. 8 provides a flowchart illustrating another exemplary method forcustomizing interactive haptic boundaries based on patient-specificdata.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or similarparts.

A healthy knee joint comprises the interface between the distal end ofthe femur and the proximal end of the tibia. If the healthy knee jointbecomes damaged due, for example, to injury or disease, knee surgery maybe required to restore normal structure and function of the joint. Ifthe damage to the knee is severe, total knee arthroplasty (“TKA”) may berequired. TKA typically involves the removal of the damaged portion ofjoint and the replacement of the damaged portion of the joint with oneor more prosthetic components.

In some TKA procedures, one or more of cruciate ligaments (includinganterior cruciate ligament and/or posterior cruciate ligament) may beleft intact, to be re-used with the prosthetic implants to form the newknee joint. In these “cruciate-retaining” applications, the prostheticimplant components may be configured to avoid interference with orimpingement on the retained cruciate ligaments passing through theintercondylar area of the knee joint. For example, each of the femoraland tibial prosthetic components may be designed with a intercondylar“notch” that extends from the posterior of the prosthetic componenttoward the anterior of the prosthetic component. The femoral and tibialintercondylar notches overlap in the vertical direction, providing apassage that allows the cruciate ligament to pass from the femoralintercondylar fossa down to the tibial eminence.

Because cruciate ligaments are exposed to significant tensile forceduring normal knee joint use, it is important that the attachment siteswhere the cruciate ligaments attach to the femur and tibia havesufficient strength to properly anchor the cruciate ligaments to thebone. Otherwise, the force applied by the cruciate ligament strains thetissue around the attachment site, possibly leading to failure of thejoint, which may require corrective surgery to repair. One way to limitthe possibility of such a failure is to limit the amount of boneresected at or near the attachment site(s) (i.e., the intercondylarfossa of the femur and tibial emmence 101 a of the tibia). Limiting theamount of disturbance of native tissue at the attachment sites helpspreserve the natural anchoring mechanism of the tissue, which decreasesthe likelihood of failure at the attachment site. As will be explainedin greater detail below, prosthetic systems consistent with thepresently disclosed embodiments may limit the amount of bone resectionthat is required for a TKA procedure. FIG. 1 illustrates a perspectiveview of a knee joint 100 fitted with a prosthetic implant system 110having a tibial implant system 120 that is configured to limit theamount of bone resection that is required at the surface of tibia 101.

In the embodiment illustrated in FIG. 1, prosthetic implant system 110may comprise a plurality of components, each of which is configured toreplace a resected portion of a native knee joint. According to oneembodiment, prosthetic implant system 110 may include a tibial implantsystem 120 configured to replace a resected portion of a native tibia101. Prosthetic implant system 110 may also include a femoral component130 configured to replace a resected portion of a native femur 102.After implantation during knee replacement surgery, tibial implantsystem 120 and femoral component 130 cooperate to replicate the form andfunction of the native knee joint.

Femoral component 130 may be secured to the distal end of femur 102 andconfigured to replace the structure and function of the native femoralportion of knee joint 100. As such, femoral component 130 may bemanufactured from surgical-grade metal or metal alloy material (such assurgical-grade steel, titanium or titanium allow, a cobalt-chromiumalloy, a zirconium alloy, or tantalum) that is substantially rigid forproviding sufficient strength to support the forces required of the kneejoint. According to one embodiment, femoral component 130 may embody asingle component having a plurality of different structural features,each configured to perform a particular function associated with theknee joint 100. For example, femoral component 130 may comprise a pairof condyles 132, each of which is coupled to a patellar guide portion133. The pair of condyles 132 may be separated from one another by anintercondylar notch 138, which provides a channel through which one ormore cruciate ligaments 103, such as anterior cruciate ligament (ACL)103 a and/or posterior cruciate ligament (PCL) 103 b, may pass.

Tibial implant system 120 may include a plurality of components thatcooperate to provide a stable surface that articulates with femoralcomponent 130 to restore proper knee joint function. As illustrated inFIG. 1, tibial implant system 120 may include a base portion 121 and oneor more insert portions 123. During a knee replacement procedure, baseportion 121 may be secured to the proximal end of the tibia 101, whichhas been surgically prepared by removing damaged bone and tissue andreshaping the healthy bone to receive the base portion 121. Once baseportion 121 is secured to tibia 101, the surgeon completes assembly oftibial implant system 120 by engaging and securing insert portions 123within base portion 121. Base portion 121 of tibial prosthetic systemmay be configured with a passage through the center to allow forconnection between the retained cruciate ligaments 103 and tibialeminence 101 a.

Base portion 121 may be configured to emulate the structure and functionof the top surface of tibia 101. Thus, similar to femoral component 130,base portion 110 may be manufactured from surgical-grade metal or metalalloy material (such as surgical-grade steel, titanium or titaniumallow, a cobalt-chromium alloy, a zirconium alloy, or tantalum) that issubstantially rigid for providing a stable base upon which toreconstruct the remainder of the prosthetic joint

Insert portions 123 may be designed to emulate the form and function ofcertain components of the natural femorotibial interface, including,among other things, medial and lateral menisci of the knee joint. Assuch, insert portions 123 may be constructed of smooth, semi-rigidsynthetic or semi-synthetic plastic, rubber, or polymer material. Insertportions 123 may be configured to provide a smooth surface that isdesigned to articulate with a femoral component 130 during normal kneeoperation. According to one embodiment, insert portions 123 areconfigured to removably engage with base portion 121. Accordingly,insert portions 123 are configured for periodic replacement if insertportions 123 deteriorate over time due, for example, to excessive wear.

In order to ensure precise and accurate preparation of the joint toreceive a prosthetic implant, CAS system may be used to generate agraphical representation of the surgical site and a correspondingvirtual guide that may aid the surgeon in properly aligning the toolprior to interaction with patient's anatomy. Many CAS systems includesoftware that allows users to electronically register certain anatomicfeatures (e.g., bones, soft tissues, etc.), surgical instruments, andother landmarks associated with the surgical site. CAS systems maygenerate a graphical representation of the surgical site based on theregistration of the anatomic features. The CAS software also allowsusers to plan certain aspects of the surgical procedure, and registerthese aspects for display with the graphical representation of thesurgical site. For example, in a knee joint replacement procedure, asurgeon may register target navigation points, the location and depth ofbone and tissue cuts, virtual boundaries that may be associated with acorresponding reference for the application of haptic force, and otheraspects of the surgery.

FIG. 2 provides a schematic diagram of an exemplary computer-assistedsurgery (CAS) system 200, in which processes and features associatedwith certain disclosed embodiments may be implemented. CAS system 200may be configured to perform a wide variety of orthopedic surgicalprocedures such as, for example, partial or total joint replacementsurgeries. As illustrated in FIG. 2, CAS system 200 may comprise atracking system 201, computer-assisted navigation system 202, one ormore display devices 203 a, 203 b, and a robotic arm 204. It should beappreciated that CAS system 200, as well as the methods and processesdescribed herein, may be applicable to many different types of jointreplacement procedures. Although certain disclosed embodiments may bedescribed with respect to knee replacement procedures, the concepts andmethods described herein may be applicable to other types of orthopedicsurgeries, such as partial hip replacement, full or partial hipresurfacing, shoulder replacement or resurfacing procedures, and othertypes of orthopedic procedures.

Robotic arm 204 can be used in an interactive manner by a surgeon toperform a surgical procedure, such as a knee replacement procedure, on apatient. As shown in FIG. 2, robotic arm 204 includes a base 205, anarticulated arm 206, a force system (not shown), and a controller (notshown). A surgical tool 210 (e.g., an end effector having an operatingmember, such as a saw, reamer, or burr) may be coupled to thearticulated arm 206. The surgeon can manipulate the surgical tool 210 bygrasping and manually moving the articulated arm 206 and/or the surgicaltool 210.

The force system and controller are configured to provide control orguidance to the surgeon during manipulation of the surgical tool. Theforce system is configured to provide at least some force to thesurgical tool via the articulated arm 206, and the controller isprogrammed to generate control signals for controlling the force system.In one embodiment, the force system includes actuators and abackdriveable transmission that provide haptic (or force) feedback toconstrain or inhibit the surgeon from manually moving the surgical toolbeyond predefined virtual boundaries defined by haptic objects asdescribed, for example, in U.S. Pat. No. 8,010,180 and/or U.S. patentapplication Ser. No. 12/654,519 (U.S. Patent Application Pub. No.2010/0170362), filed Dec. 22, 2009, each of which is hereby incorporatedby reference herein in its entirety. According to one embodiment, CASsystem 200 is the RIO® Robotic Arm Interactive Orthopedic Systemmanufactured by MAKO Surgical Corp. of Fort Lauderdale, Fla. The forcesystem and controller may be housed within the robotic arm 204.

Tracking system 201 may include any suitable device or system configuredto track the relative locations, positions, orientations, and/or posesof the surgical tool 210 (coupled to robotic am 204) and/or positions ofregistered portions of a patient's anatomy, such as bones. Such devicesmay employ optical, mechanical, or electromagnetic pose trackingtechnologies. According to one embodiment, tracking system 201 maycomprise a vision-based pose tracking technology, wherein an opticaldetector, such as a camera or infrared sensor, is configured todetermine the position of one or more optical transponders (not shown).Based on the position of the optical transponders, tracking system 201may capture the pose (i.e., the position and orientation) information ofa portion of the patient's anatomy that is registered to thattransponder or set of transponders.

Navigation system 202 may be communicatively coupled to tracking system201 and may be configured to receive tracking data from tracking system201. Based on the received tracking data, navigation system 202 maydetermine the position and orientation associated with one or moreregistered features of the surgical environment, such as surgical tool210 or portions of the patient's anatomy. Navigation system 202 may alsoinclude surgical planning and surgical assistance software that may beused by a surgeon or surgical support staff during the surgicalprocedure. For example, during a joint replacement procedure, navigationsystem 202 may display images related to the surgical procedure on oneor both of the display devices 203 a, 203 b.

Navigation system 202 (and/or one or more constituent components of CASsystem 200) may include or embody a processor-based system (such as ageneral or special-purpose computer) in which processes and methodsconsistent with the disclosed embodiments may be implemented. Forexample, as illustrated in FIG. 3, CAS system 200 may include one ormore hardware and/or software components configured to execute softwareprograms, such as, tracking software, surgical navigation software, 3-Dbone modeling or imaging software, and/or software for establishing andmodifying virtual haptic boundaries for use with a force system toprovide haptic feedback to surgical tool 210. For example, CAS system200 may include one or more hardware components such as, for example, acentral processing unit (CPU) (processor 231); computer-readable media,such as a random access memory (RAM) module 232, a read-only memory(ROM) module 233, and a storage device 234; a database 235; one or moreinput/output (I/O) devices 236; and a network interface 237. Thecomputer system associated with CAS system 200 may include additional,fewer, and/or different components than those listed above. It isunderstood that the components listed above are exemplary only and notintended to be limiting.

Processor 231 may include one or more microprocessors, each configuredto execute instructions and process data to perform one or morefunctions associated with CAS system 200. As illustrated in FIG. 3,processor 231 may be communicatively coupled to RAM 232, ROM 233,storage device 234, database 235, I/O devices 236, and network interface237. Processor 231 may be configured to execute sequences of computerprogram instructions to perform various processes, which will bedescribed in detail below. The computer program instructions may beloaded into RAM for execution by processor 231.

Computer-readable media, such as RAM 232, ROM 233, and storage device234, may be configured to store computer-readable instructions that,when executed by processor 231, may cause CAS system 200 or one or moreconstituent components, such as navigation system 202, to performfunctions or tasks associated with CAS system 200. For example, computerreadable media may include instructions for causing the CAS system 200to perform one or more methods for determining changes in parameters ofa hip joint after a hip arthroplasty procedure. Computer-readable mediamay also contain instructions that cause tracking system 201 to capturepositions of a plurality of anatomical landmarks associated with certainregistered objects, such as surgical tool 210 or portions of a patient'sanatomy, and cause navigation system 202 to generate virtualrepresentations of the registered objects for display on I/O devices236. Exemplary methods for which computer-readable media may containinstructions will be described in greater detail below. It iscontemplated that each portion of a method described herein may havecorresponding instructions stored in computer-readable media for causingone or more components of CAS system 200 to perform the methoddescribed.

I/O devices 236 may include one or more components configured tocommunicate information with a user associated with CAS system 200. Forexample, I/O devices 236 may include a console with an integratedkeyboard and mouse to allow a user (e.g., a surgeon) to input parameters(e.g., surgeon commands 250) associated with CAS system 200. I/O devices236 may also include a display, such as monitors 203 a, 203 b, includinga graphical user interface (GUI) for outputting information on amonitor. I/O devices 236 may also include peripheral devices such as,for example, a printer for printing information associated with CASsystem 200, a user-accessible disk drive (e.g., a USB port, a floppy,CD-ROM, or DVD-ROM drive, etc.) to allow a user to input data stored ona portable media device, a microphone, a speaker system, or any othersuitable type of interface device. For example, I/O devices 236 mayinclude an electronic interface that allows a user to input patientcomputed tomography (CT) data 260 into CAS system 200. This CT data maythen be used to generate and manipulate virtual representations ofportions of the patient's anatomy (e.g., a virtual model of a tibia 101)in software.

Software associated with CAS system 200 may be configured to enablesurgical planning, navigation, and basic image guided surgerycapabilities. For example, as is well known, software associated withCAS system 200 may include computer-implemented processes for generatingand displaying images (either captured images or computer-generatedcaptured images) from image data sets, computer-implemented processesfor determining a position of a tip and an orientation of an axis of asurgical instrument, and computer-implemented processes for registeringa patient and an image data set to a coordinate frame of the trackingsystem 201. These processes may enable, for example, the CAS system 200to display on the display device(s) 203 a, 203 b a virtualrepresentation of a tracked surgical instrument (and/or a prostheticimplant) overlaid on one or more images of a patient's anatomy and toupdate the virtual representation of the tracked instrument in real-timeduring a surgical procedure. Images generated from the image data setmay be two-dimensional or, in the case of a three-dimensional image dataset, a three-dimensional reconstruction based, for example, onsegmentation of the image data set. According to one embodiment, imagesassociated with the image data set may include CT scan data associatedwith a patient's anatomy, a prosthetic implant, or any object. When morethan one image is shown on the display device(s) 203 a, 203 b, the CASsystem 200 may coordinate the representation of the tracked instrumentamong the different images.

According to another embodiment, an imageless system may be utilized togenerate and manipulate virtual representations of portions of thepatient's anatomy (e.g., a virtual model of a tibia 101) in software.Imageless systems include technologies that are well-known in the art,such as systems utilizing statistically shaped models and methods ofbone morphing. In one form of imageless system, a virtual representationof a portion of the patient's anatomy is created based onpatient-specific characteristics (such as anatomical landmarks obtainedby physically touching the patient's anatomy using a probe tool). Inother imageless systems, a three-dimensional virtual representation of aportion of the patient's anatomy is obtained by selecting athree-dimensional model from a database or library of bone models. Theselected bone model can then be deformed based on patient-specificcharacteristics, creating a three-dimensional representation of thepatient's anatomy.

Processor 231 associated with CAS system 200 may be configured toestablish a virtual haptic geometry associated with or relative to oneor more features of a patient's anatomy. As explained, CAS system 200may be configured to create a virtual representation of a surgical sitethat includes, for example, virtual representations of a patient'sanatomy, a surgical instrument to be used during a surgical procedure, aprobe tool for registering other objects within the surgical site, andany other such object associated with a surgical site.

In addition to physical objects, CAS system 200 may be configured togenerate virtual objects that exist in software and may be useful duringthe performance of a surgical procedure. For example, CAS system 200 maybe configured to generate virtual boundaries that correspond to asurgeon's plan for preparing a bone, such as boundaries defining areasof the bone that the surgeon plans to cut, remove, or otherwise alter.Alternatively or additionally, CAS system 200 may define virtual objectsthat correspond to a desired path or course over which a portion ofsurgical tool 210 should navigate to perform a particular task.

Virtual boundaries and other virtual objects may define a point, line,or surface within a virtual coordinate space (typically defined relativeto an anatomy of a patient) that serves as a boundary at which hapticfeedback is provided to a surgical instrument when the tracked positionof the surgical instrument interacts with the virtual boundary orobject. For example, as the surgeon performs a bone cutting operation,tracking system 201 of CAS system 200 tracks the location of the cuttingtool and, in most cases, allows the surgeon to freely move the tool inthe workspace. However, when the tool is in proximity to a virtualhaptic boundary (that has been registered to the anatomy of thepatient), CAS system 200 controls the force feedback system to providehaptic guidance that tends to constrain the surgeon from penetrating thevirtual haptic boundary with the cutting tool. For example, a virtualhaptic boundary may be associated with the geometry of a virtual modelof a prosthetic implant, and the haptic guidance may comprise a forceand/or torque that is mapped to the virtual boundary and experienced bythe surgeon as resistance to constrain tool movement from penetratingthe virtual boundary. Thus, the surgeon may feel as if the cutting toolhas encountered a physical object, such as a wall. In this manner, thevirtual boundary functions as a virtual cutting guide. Accordingly, theforce feedback system of CAS system 200 communicates information to thesurgeon regarding the location of the tool relative to the virtualboundary, and provides physical force feedback to guide the cutting toolduring the actual cutting process. The force feedback system of CASsystem 200 may also be configured to limit the user's ability tomanipulate the surgical tool.

Systems and methods consistent with the disclosed embodiments provide asolution for customizing a virtual haptic boundary and providing ahaptic feedback for guiding the surgical instrument. According to oneembodiment, the virtual haptic boundary may be customized based on auser request to modify a default boundary associated with acorresponding implant geometry. Alternatively or additionally, thevirtual haptic boundary may be customized based, at least in part, on adetection of the patient's anatomy (e.g., a location of soft tissue, theedge perimeter of a bone, etc.). The process for customizing the virtualhaptic boundary may be part of an implant planning phase, during whichthe surgeon pre-operatively or intra-operatively plans the placement ofprosthetic implants and the corresponding modification/removal of jointtissue to accommodate the implant. FIGS. 4 and 5 provide exemplaryscreen shots of a graphical user interface associated with planningsoftware for CAS system 200.

FIG. 4 illustrates an exemplary screen shot 400 associated with agraphical user interface screen of planning software associated with CASsystem 200. As illustrated in FIG. 4, planning software may includevirtual models of prosthetic implants, such as a tibial base portion 121associated with tibial implant system 120. According to one embodiment,a virtual implant model may be provided by the manufacturer of theprosthetic implant and may provide a graphical representation of thegeometry of the prosthetic implant. Using the graphical representationof the geometry, a virtual haptic boundary may be created and associatedwith the virtual implant model.

The graphical user interface 400 may include a plurality of sub-screens,each of which is configured to display a particular feature of theimplant planning. For example, graphical user interface 400 may includea first sub-screen (e.g., upper left) for displaying the selectedvirtual implant model (e.g., a model associated with tibia base portion121). Graphical user interface 400 may include a second sub-screen(upper right) for displaying the virtual model associated with thepatient's anatomy (e.g., tibia 101) upon which the implant will bepositioned. Graphical user interface 400 may include a third sub-screen(lower left) for displaying the planned placement of virtual implantmodel within the patient's anatomy. Graphical user interface 400 mayalso include a fourth sub-screen (lower right) for displaying a view ofrespective medial and lateral resection portions 401 a, 401 b associatedwith the planned implant placement. It is contemplated that the numberand view of sub-screens may differ from those provided in the exemplaryembodiment illustrated in FIG. 4. It is also contemplated that one ormore of the sub-screens allow a user to interactively update the viewand/or the components within the view. For example, although the lowerright screen shows a top view of the simulated resection of thepatient's tibia 101 based on the planned implant placement shown in thelower left sub-screen, it is contemplated that the user can selectdifferent views (e.g., front, back, side, bottom, etc.) for displayingthe contents of the sub-screen.

FIG. 5 provides an alternative embodiment of a graphical user interface500 associated with planning software of CAS system 200. According tothe embodiment shown in FIG. 5, graphical user interface 500 embodies aninteractive interface that allows the user to manipulate the position ofa prosthetic implant and/or a virtual haptic boundary associatedtherewith. For example, FIG. 5 provides a rear-view of a virtual modelassociated with tibial base portion 121 (including medial implantportions 121 a and lateral implant portion 121 b), which has beenpositioned atop a virtual model of the patient's tibia 101.

Graphical user interface 500 may also display a reference feature 505associated with the virtual implant model. As illustrated in FIG. 5,reference feature 505 may correspond with the plane defined by thebottom surfaces of medial and lateral base portions 121 a, 121 b. It iscontemplated, however, that reference feature 505 may include or embodyany feature (e.g., point, line, or surface) of virtual implant modelthat defines a reference to which modifications will be made to thevirtual haptic boundary.

Using graphical user interface 500, users can modify the virtual hapticboundary that is used for virtually guiding a cutting tool to preparethe bone for placement of a prosthetic implant. For example, apreliminary virtual haptic boundary may be associated with the virtualimplant model and designed to substantially match the geometryassociated with the virtual implant (e.g., medial and lateral baseportions 121 a, 121 b). This preliminary virtual haptic boundary may bestretched or contracted to, for example, accommodate certain anatomicfeature(s) associated with the patient's anatomy.

To modify the preliminary virtual haptic boundary, the user may identifyone or more anatomical features associated with the patient's anatomy.For example, a surgeon may wish to stretch outer edges of virtual hapticboundaries associated with medial and lateral base portions 121 a, 121 bto allow bone resection to the outer perimeter of the patient's tibia101. As such, a user may select (or planning software may detect) points510, 512 associated with the perimeter of tibia 101. The planningsoftware may stretch the outer edges of the preliminary virtual hapticboundaries of medial and lateral base portions 121 a, 121 b to points510, 512, respectively. As will be explained in greater detail below,planning software associated with CAS system 200 may identify theintersecting or overlapping areas between the stretched boundary and thepatient's anatomy and establish a new, modified virtual haptic boundarybased on the extent of the overlapping area(s).

In addition to stretching the virtual haptic boundary, planning softwareassociated with CAS system may also be configured to contract thepreliminary virtual boundary to avoid certain sensitive anatomicalfeatures. For example, a surgeon may wish to contract the inner edges ofvirtual haptic boundaries associated with medial and lateral baseportions 121 a, 121 b to limit the operation of the cutting tool nearthe tibial eminence 101 a, and avoid the possibility of inadvertentlydamaging soft tissues (e.g., ACL or PCL) that attach thereto. Thesurgeon may use other cutting tools and/or methods to carefully andmanually prepare such critical areas.

As shown in FIG. 5, in order to avoid the area surrounding tibialeminence 101 a, the user may establish anatomic landmarks 520, 522corresponding to the inner edges of medial and lateral base portions 121a, 121 b, respectively. The planning software may contract the inneredges of the preliminary virtual haptic boundaries of medial and lateralbase portions 121 a, 121 b to points 520, 522, respectively. As will beexplained in greater detail below, planning software associated with CASsystem 200 may identify the intersecting or overlapping areas betweenthe contracted boundary and the patient's anatomy and establish a new,modified virtual haptic boundary based on the extent of the overlappingarea(s).

FIG. 6 provides a flowchart 600 that illustrates an exemplary method forgenerating a patient-specific virtual haptic boundary. According to oneembodiment, the method illustrated in FIG. 6 may be implemented duringan implant placement planning stage associated with the performance of asurgical procedure. The planning stage may be performed pre-operativelyby a surgeon or other medical professional, prior to commencement of thesurgical procedure. Alternatively or additionally, the planning stagemay be performed (or repeated) intra-operatively, during the medicalprocedure.

During the implant planning stage, a surgeon or medical professional mayuse planning software associated with CAS system 200 to plan theplacement of prosthetic implants onto or within a patient's anatomy. Assuch, virtual (i.e., software) 3-D models of prosthetic implants, thepatient's anatomy, a surgical instrument (such as cutting tool(s)), andany other physical object that may be used during the surgical proceduremay be generated and registered to a virtual coordinate space (generallyone that corresponds with the patient's anatomy). Using planningsoftware, the surgeon can virtually position a prosthetic implantrelative to the patient's anatomy. Once the placement has beenfinalized, the surgeon can then register one or more reference featuresassociated with virtual implant to the patient's anatomy to provide thesurgeon with a graphical view to show how the patient's anatomy can bemodified to accommodate the planned placement of the implant.

As illustrated in flowchart 600 of FIG. 6, once the implant has beenplaced in a desired position relative to the patient's anatomy, themethod may commence by identifying the position and orientation of areference feature associated with the virtual implant model in thevirtual coordinate space (Step 610). The reference feature of thevirtual implant model may embody one or more points, lines, planes, orsurfaces of the virtual implant model and, by extension, the prostheticmodel associated therewith. As illustrated in the embodiment illustratedin FIG. 5, the reference feature may be a reference plane 505 defined bythe bottom surfaces of medial and lateral base portions 121 a, 121 btibial implant system 120. Alternatively or additionally, the referencefeature may include or embody any feature associated with the implantthat the surgeon wishes to use as the reference with which to customizevirtual haptic boundaries.

Once the reference feature associated with the virtual implant model hasbeen established, an intersection between the identified referencefeature and virtual model of the patient's anatomy may be determined(Step 620). For example, as illustrated in FIG. 5, planning softwareassociated with CAS system 200 may be configured to determine areaswhere the surfaces of medial base portion 121 a and lateral base portion121 b intersect and/or overlap the virtual model of the patient's tibia101. According to one embodiment, processor 231 of CAS system 200 may beconfigured to calculate, based on the position of virtual implant modelrelative to the virtual model associated with the patient's anatomy, theoverlapping volume between the virtual implant model and the virtualmodel of the patient's anatomy.

Upon identifying the overlapping volume between the virtual implantmodel and the virtual model of the patient's anatomy, planning softwareof CAS system 200 may be configured to generate a preliminary virtualhaptic boundary based, at least in part, on the determined intersectionbetween the virtual implant model and the patient-specific anatomicmodel (Step 630). This preliminary virtual haptic boundary typicallycorresponds closely with the geometric shape of the prosthetic implant.According to one embodiment, however, it may differ slightly from thegeometry of the implant. For example, the preliminary virtual hapticboundary may be slightly larger than the prosthetic implant to allowsufficient space for surgical tool access (e.g., to accommodate for thewidth of a cutting tool) or to provide an area for entering the volumedefined by the virtual haptic boundary.

Once generated, the preliminary virtual haptic boundary may beregistered to the patient's anatomy and displayed on display 203 a, 203b of CAS system 200 (Step 640). Specifically, when the preliminaryvirtual haptic boundary is generated based on the relative position ofthe virtual implant model within the virtual coordinate space, planningsoftware associated with CAS system 200 may be configured to map thevirtual surfaces and features that define the virtual haptic boundary tothe virtual coordinate space associated with the patient's anatomy. Assuch, the boundary surfaces associated with the virtual haptic boundarybecome linked to the patient's anatomy, thereby defining the areas ofthe patient's anatomy within which the surgical instrument is permittedto operate. By registering the virtual haptic boundary to the patient'sanatomy, the preliminary virtual haptic boundary becomes virtuallylinked to the patient's anatomy, so that the virtual haptic boundary canbe tracked (and viewed) relative to the specific movements,modifications, and adjustments in the patient's anatomy during thesurgical procedure.

Upon displaying the preliminary virtual haptic boundary, planningsoftware associated with CAS system 200 may be configured to allow auser to make modifications to the virtual haptic boundary to moreappropriately account for certain features that are specific to thepatient's anatomy. FIG. 7 provides a flowchart 700 illustrating anexemplary method for further customizing a virtual haptic boundarybased, at least in part, on certain anatomic features associated with apatient. According to an exemplary embodiment, the method illustrated inFIG. 7 can be performed as an optional extension of the exemplaryplanning method for establishing the preliminary virtual haptic boundaryillustrated in FIG. 6.

Alternatively or additionally, the method illustrated in FIG. 7 may beperformed as a standalone process for modifying an established virtualhaptic boundary. For example, during a pre-operative planning phase, thesurgeon may develop and approve a surgical plan. As part of thispre-operative planning phase, the surgeon may establish a virtual hapticboundary associated with the pre-operative plan. Later, perhaps during aseparate, intra-operative process, the surgeon may, using the processconsistent with the flowchart shown in FIG. 7, modify the existingvirtual haptic boundary that was previously established during thepre-operative planning phase. As a result, processes and methodsconsistent with the disclosed embodiments allow a user (e.g., a surgeonor other medical professional) to modify the virtual haptic boundary inreal-time in order to customize the virtual boundary based on thepatient-specific parameters.

As illustrated in FIG. 7, the method for customizing the virtual hapticboundary may commence upon receipt of information indicative of ananatomical landmark (or other designated feature) associated with avirtual model of the patient's anatomy (Step 710). According to oneembodiment, the anatomical landmark may be automatically identifiedbased on a geometry associated with the virtual model of the patient'sanatomy. For example, planning software associated with CAS system 200may be configured to automatically detect an anatomic feature associatedwith the patient's anatomy such as, for example, a perimeter of apatient's bone (e.g., tibia 101), the location of a particularprotrusion associated with the patient's bone (e.g., tibial eminence 101a), or any other specific feature associated with the patient's anatomy.This feature for automatically detecting an anatomical landmark may bebased on a surface analysis process performed by planning software,whereby the surface of the 3-D model associated with the patient'sanatomy is scanned for surface discontinuities (e.g., a dramaticdrop-off in height at the perimeter of the patient's bone) orprotrusions (e.g., a dramatic increase in the surface height of thebone).

As an alternative or in addition to automatic detection, informationindicative of anatomical landmarks may be received based on a userinput. For example, a surgeon may designate one or more points, lines,or areas of the patient's anatomy as anatomical landmarks manually byphysically touching the points, lines, or areas of the patient's anatomyusing a probe tool that has been registered with the virtual coordinatespace. According to another embodiment, a user of CAS system 200 mayinput information associated with anatomical landmarks using a graphicaluser interface associated with planning software. Specifically, a usermay select, via a graphical user interface, one or more points, lines,surfaces, or areas on a 3-D virtual model of the patient's anatomy usinga mouse or other input device.

FIG. 5 illustrates a plurality of exemplary anatomical landmarksassociated with tibia 101, which may be established as part of anexemplary surgical procedure for implanting a tibial prosthetic system120. As illustrated in FIG. 5, anatomical landmarks 510, 512 may beassociated with a perimeter of tibia 101. According to one embodiment,the perimeter of tibia 101 may be established as the perimeter of theupper surface of tibia 101 (as with anatomical landmark 510). In certainembodiments, however, the perimeter of tibia 101 may be allowed toextend beyond the end of the surface of tibia 101 (as with anatomicallandmark 512) to account for portions of tibia 101 that may extendlaterally beyond the surface of tibia 101 (such as anatomical landmark517).

FIG. 5 also illustrates exemplary anatomical landmarks 520, 522 that maybe associated with certain protrusions associated with the patient'sanatomy. As illustrated in FIG. 5, anatomical landmarks 520, 522 maycorrespond with areas surrounding tibial eminence 101 a and/or otherareas that a surgeon wishes to protect during the bone resectionprocess.

Returning to FIG. 7, once information indicative of patient-specificanatomical landmarks has been received, the intersection between theanatomical landmark and a reference feature associated with the virtualimplant model may be determined (Step 720). As explained, referencefeature 505 may be designated as the plane defined by the medial andlateral base portions 121 a, 121 b, which ultimately define the depth ofbone resection of tibia that is required to accommodate the plannedplacement of the tibial implant.

Planning software associated with CAS system 200 may be configured toestimate the intersection between the selected anatomical landmarks 510,512, 520, 522 and the reference feature 505. According to oneembodiment, each of intersection points 515, 517, 525, 527 may beestimated as the closest point along reference feature 505 tocorresponding anatomical landmarks 510, 517, 520, 522, respectively.Alternatively or additionally, intersection points 515, 517, 525, 527may be estimated based on the anatomical profile of the patient'sanatomy. For example, intersection points 515 and 517 associated withanatomical landmarks 510 and 512 may be estimated based on theintersection between the perimeter of the bone and the reference feature505.

Turning back to FIG. 7, upon estimating the intersection between theanatomical landmark(s) and reference feature associated with the virtualimplant model, planning software associated with CAS system 200 may beconfigured to modify the virtual haptic boundary based, at least inpart, on the estimated intersection (Step 730). According to oneembodiment, the modified haptic boundary may be established bystretching (or contracting) a surface associated with the preliminaryvirtual haptic boundary to one or more of anatomical landmarks 510, 512,520, 522. Planning software associated with CAS system 200 may thenmodify the virtual haptic boundary based on the overlap between thestretched (or contracted) surface and the virtual model of the patient'sanatomy to generate a new, patient-specific virtual haptic boundarybased on the overlapping area(s). CAS system 200 may then apply thevirtual haptic boundary to surgical instrument, and display the modifiedvirtual haptic boundary on display devices 203 a, 203 b (Step 740).

FIG. 8 provides a flowchart 800 showing another exemplary method forcustomizing a haptic boundary based on patient-specific parameters. Asillustrated in FIG. 8, the method may commence upon receipt ofpre-operative image(s) or image data associated with a patient's anatomy(Step 805). Pre-operative image(s) may include any two- orthree-dimensional image data set obtained using any suitable imagingprocess for recording images associated with a patient's anatomy suchas, for example, x-ray, computed tomography (CT), magnetic resonance(MR), positron emission tomography (PET), single photon emissioncomputed tomography (SPECT), ultrasound, etc. According to oneembodiment, I/O devices 236 of CAS system 200 may receive pre-operativeCT scan data 260 associated with the anatomy of the specific patientthat is to be operated on.

Upon receiving pre-operative image of the anatomy of a patient, softwareassociated with CAS system 200 may generate a 3-D virtual model of thepatient's anatomy (Step 810). For example, CAS system 200 may includeone of a number of different software tools for rendering 3-D models ofobjects, based on the received 2-D (or 3-D) image data sets associatedwith the anatomy of the patient. In an alternative embodiment, the 3-Dvirtual model of the patient's anatomy is generated utilizing animageless system.

After the virtual model of the patient's anatomy is generated, it may beregistered with the actual anatomy of the patient so that CAS system 200can virtually track the position and orientation of the actual anatomyof the patient in virtual software space. According to one embodiment,this registration process involves associating a plurality of points ofthe patient's anatomy with corresponding points on the virtual model. Asexplained above, such associations can be made using a probe tool thathas been registered in the virtual coordinate space, whereby a pluralityof points on the patient's anatomy gathered by touching or “exploring”one or more surfaces of the patient's anatomy using the tip of the probetool. Once the virtual model is registered with the patient's anatomy,CAS system 200 may be able to track the position and orientation of thepatient's anatomy in the virtual coordinate space.

After the 3-D virtual model of the patient's anatomy is generated andregistered to the patient's bone, planning software of CAS system 200may be configured to facilitate the planning of an prosthetic implantwithin the patient's anatomy (Step 815). Specifically, planning softwareof CAS system 200 may be configured to determine, based on a user input,placement of a virtual implant model relative to the virtual model ofthe patient's anatomy. For example, a surgeon may select a virtualimplant model (e.g., virtual model associated with tibial base portion121 as shown in FIG. 4) from a database of implants available for thesurgery. Using a graphical user interface 400, the surgeon maymanipulate the position of the virtual implant model relative to thepatient's anatomy (e.g., tibia 101), which produces a virtualrepresentation of the tibia fitted with the virtual implant, as shown inthe lower left sub-screen of graphical user interface 400 of FIG. 4.Such a process for virtually planning implant placement allows thesurgeon to make precise adjustments to the position of the implantrelative to the patient's anatomy in a simulated software environment,prior to commencing the bone resection process.

Once the placement of the virtual implant model with respect to thevirtual model of the patient's anatomy is finalized, the referencesurface information may be extracted from the virtual implant model(Step 820). According to one embodiment, the reference surface of thevirtual implant model may embody one or more points, lines, planes, orsurfaces of the virtual implant model. As illustrated in the embodimentillustrated in FIG. 5, the reference feature may be a reference plane505 defined by the bottom surfaces of medial and lateral base portions121 a, 121 b of a base portion 121 of tibial implant system 120.Alternatively or additionally, the reference surface may include orembody any feature associated with the implant that the surgeon wishesto use as the reference with which to customize virtual hapticboundaries. For example, reference surface may include any surfaceassociated with the virtual implant model that directly abuts or faces asurface of the virtual model associated with the patient's anatomy.

Upon extracting the reference surface information, planning softwareassociated with CAS system 200 may map the reference surface informationonto the coordinate space of the patient's anatomy (Step 825). That is,planning software associated with CAS system 200 may register thereference surfaces of the virtual implant model to the virtual model ofthe patient's bone, such that the reference surfaces are trackedrelative to the position of the patient's bone.

Planning software of CAS system 200 may be configured to determine theintersection between the mapped reference surface and the patient'sanatomy, and virtually resect tissue based on the determinedintersection (Step 830). The lower right-hand sub-screen of graphicaluser interface 400 of FIG. 4 illustrates respective medial and lateralresection portions 401 a, 401 b of the patient's bone that have beenresected based on the intersection between the reference surface of thevirtual implant model and the virtual model associated with thepatient's anatomy. As illustrated in FIG. 4, the implant-specificreference surface has been transferred to the patient-specificanatomical model and, based on the intersection between the twosurfaces, the patient-specific resection region associated with thegeneric implant model may be identified.

Planning software of CAS system 200 may also be configured to generate apreliminary virtual haptic boundary based on the intersection betweenthe reference surface associated with the virtual implant model and thevirtual model of the patient's anatomy (Step 835). For example, uponidentifying the overlapping volume between the reference surfaces ofvirtual implant model and the virtual model of the patient's anatomy,planning software of CAS system 200 may be configured to generate avirtual haptic boundary based, at least in part, on the identifiedoverlapping volume. This preliminary virtual haptic boundary typicallycorresponds closely with the geometric shape of the prosthetic implant.According to some embodiments, however, it may differ slightly from thegeometry of the implant. For example, the preliminary virtual hapticboundary may be slightly larger than the prosthetic implant to allowsufficient space for surgical tool access (e.g., to accommodate for thewidth of a cutting tool) or to provide an area for entering the volumedefined by the virtual haptic boundary.

Upon generating the preliminary virtual haptic boundary, planningsoftware of CAS system 200 may provide the user with an option tofinalize the virtual haptic boundary (Step 840). If the user decides tofinalize the virtual haptic boundary (Step 840: Yes), CAS system 200 mayupdate the force system with the coordinates of virtual haptic boundary.As such, CAS system 200 may be configured to selectively apply thevirtual haptic forces to surgical instrument based on the trackedposition of the surgical instrument relative to the virtual hapticboundary (Step 845).

If, on the other hand, the user elects instead to modify the virtualhaptic boundary (Step 840: No), planning software of CAS system 200 mayreceive information for modifying the virtual haptic boundary (Step850). Information for modifying the virtual haptic boundary may bereceived automatically (based on a particular anatomic feature),manually (based on a user input for modifying the boundary), or acombination of both automatic and manual methods.

For example, planning software associated with CAS system 200 may beconfigured to automatically detect an anatomic feature associated withthe patient's anatomy such as, for example, a perimeter of a patient'sbone (e.g., tibia 101), the location of a particular protrusionassociated with the patient's bone (e.g., tibial eminence 101 a), or anyother specific feature associated with the patient's anatomy. Thisfeature for automatically detecting an anatomical landmark may be basedon a surface analysis process performed by planning software, wherebythe surface of the 3-D model associated with the patient's anatomy isscanned for surface discontinuities (e.g., a dramatic drop-off in heightat the perimeter of the patient's bone) or protrusions (e.g., a dramaticincrease in the surface height of the bone).

As an alternative or in addition to automatic detection, informationindicative of anatomical landmarks may be received based on a userinput. For example, a surgeon may designate one or more points, lines,or areas of the patient's anatomy as anatomical landmarks manually byphysically touching the points, lines, or areas of the patient's anatomyusing a probe tool that has been registered with the virtual coordinatespace. According to another embodiment, a user of CAS system 200 mayinput information associated with anatomical landmarks using a graphicaluser interface associated with planning software. Specifically, a usermay select, via a graphical user interface, one or more points, lines,surfaces, or areas on a 3-D virtual model of the patient's anatomy usinga mouse or other input device.

Based on the received information, planning software associated with CASsystem 200 may be configured to modify the virtual haptic boundarybased, for example, on the estimated intersection between the anatomicallandmarks and the reference feature (Step 855). Using FIG. 5 as anexample, the modified haptic boundary may be established by stretching(or contracting) a surface associated with the preliminary virtualhaptic boundary (which may be associated with the geometry of a virtualimplant) to one or more of anatomical landmarks 510, 512, 520, 522.Planning software associated with CAS system 200 may then modify thevirtual haptic boundary based on the overlap between the stretched (orcontracted) surface and the patient's anatomy to generate a new,patient-specific virtual haptic boundary based on the overlappingarea(s).

The presently disclosed systems and methods for customizing virtualhaptic boundaries provide a solution for easily adjusting virtual hapticboundaries associated with force feedback control system forcomputer-assisted surgery systems. According to one embodiment, thissolution allows a user to easily modify a haptic boundary by stretchingor contracting an existing haptic boundary to fit one or more anatomicallandmarks. The planning software may then determine an intersectionbetween the stretched (or contracted) boundary and the virtual model ofthe patient's anatomy to define the location of the new virtual hapticboundary, and establish the new virtual haptic boundary based on thedetermined intersection.

The foregoing descriptions have been presented for purposes ofillustration and description. They are not exhaustive and do not limitthe disclosed embodiments to the precise form disclosed. Modificationsand variations are possible in light of the above teachings or may beacquired from practicing the disclosed embodiments. For example, thedescribed implementation includes software, but the disclosedembodiments may be implemented as a combination of hardware and softwareor in firmware. Examples of hardware include computing or processingsystems, including personal computers, servers, laptops, mainframes,microprocessors, and the like. Additionally, although disclosed aspectsare described as being stored in a memory, one skilled in the art willappreciate that these aspects can also be stored on other types ofcomputer-readable storage devices, such as secondary storage devices,like hard disks, floppy disks, a CD-ROM, USB media, DVD, or other formsof RAM or ROM.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed systems andassociated methods for customizing interactive haptic boundaries basedon patient-specific data. Other embodiments of the present disclosurewill be apparent to those skilled in the art from consideration of thespecification and practice of the present disclosure. It is intendedthat the specification and examples be considered as exemplary only,with a true scope of the present disclosure being indicated by thefollowing claims and their equivalents.

What is claimed is:
 1. A method for customizing an interactive boundarybased on a patient-specific feature, comprising: displaying a graphicalrepresentation of an implant in virtual coordinate space; displaying agraphical representation of a bone in virtual coordinate space;positioning the graphical representation of the implant relative to thegraphical representation of the bone based on a user input; extractingreference feature information associated with the virtual representationof the implant; mapping the extracted reference feature information tothe graphical representation of the bone; receiving informationindicative of a positional landmark associated with the bone; estimatingan intersection between the positional landmark and the mapped referencefeature; and generating a virtual boundary based, at least in part, onthe estimated intersection between the positional landmark and themapped reference feature.
 2. The method of claim 1, wherein thereference feature information includes a position and orientation of asurface of the graphical representation of the implant that abuts thegraphical representation of the bone.
 3. The method of claim 2, whereinthe surface includes the bottom surface of the graphical representationof the implant.
 4. The method of claim 1, wherein the virtual implantmodel includes a virtual model of a tibial prosthetic base, wherein thereference feature includes a bottom surface of the tibial prostheticbase.
 5. The method of claim 3, wherein the positional landmark includesa perimeter of the bone and estimating the intersection includescalculating the intersection between the perimeter of the bone and thebottom surface of the graphical representation of the implant.
 6. Themethod of claim 3, wherein the positional landmark includes auser-defined landmark for adjusting the virtual boundary.
 7. The methodof claim 1, wherein generating the virtual boundary includes: retrievinga default virtual boundary corresponding to the geometry of thegraphical representation of the implant; determining a differencebetween a position of a portion of the default virtual boundary and thepositional landmark associated with the bone; and generating a modifiedboundary based, at least in part, on the determined difference betweenthe position of the portion of the default virtual boundary and thepositional landmark associated with the bone.
 8. The method of claim 1,further comprising: receiving information indicative of a numericaloffset based on a user input; and generating a modified boundary based,at least in part, on the received numerical offset information.
 9. Themethod of claim 1, further comprising: receiving a signal indicative ofa user-defined modification to the generated virtual haptic boundary;and modifying the generated virtual haptic boundary based on thereceived signal.
 10. The method of claim 1, further comprising:receiving computed tomography (CT) data associated with the patient'sanatomy; and generating the virtual model associated with the patient'sanatomy based on the CT data.
 11. The method of claim 1, wherein thevirtual boundary is a virtual haptic boundary.
 12. A computer-assistedsurgery system comprising: a display; an input device configured toreceive data input by a user; a processor, operatively coupled to theinput device and the display and configured to: display, on the display,a graphical representation of an implant in virtual coordinate space;display, on the display, a graphical representation of a bone in virtualcoordinate space; position the graphical representation of the implantrelative to the graphical representation of the bone based on a userinput; extract reference feature information associated with the virtualrepresentation of the implant; map the extracted reference featureinformation to the graphical representation of the bone; receiveinformation indicative of a positional landmark associated with thebone; estimate an intersection between the positional landmark and themapped reference feature; and generate a virtual boundary based, atleast in part, on the estimated intersection between the positionallandmark and the mapped reference feature.
 13. The computer-assistedsurgery system of claim 12, wherein the reference feature informationincludes a position and orientation of a surface of the graphicalrepresentation of the implant that abuts the graphical representation ofthe bone.
 14. The computer-assisted surgery system of claim 13, whereinthe surface includes the bottom surface of the graphical representationof the implant.
 15. The computer-assisted surgery system of claim 14,wherein the positional landmark includes a perimeter of the bone andestimating the intersection includes calculating the intersectionbetween the perimeter of the bone and the bottom surface of thegraphical representation of the implant.
 16. The computer-assistedsurgery system of claim 14, wherein the positional landmark includes auser-defined landmark for adjusting the virtual boundary.
 17. Thecomputer-assisted surgery system of claim 12, wherein generating thevirtual boundary includes: retrieving a default virtual boundarycorresponding to the geometry of the graphical representation of theimplant; determining a difference between a position of a portion of thedefault virtual boundary and the positional landmark associated with thebone; and generating a modified boundary based, at least in part, on thedetermined difference between the position of the portion of the defaultvirtual boundary and the positional landmark associated with the bone.18. The computer-assisted surgery system of claim 12, wherein theprocessor is further configured to: receive a signal indicative of auser-defined modification to the generated virtual haptic boundary; andmodify the generated virtual haptic boundary based on the receivedsignal.
 19. The computer-assisted surgery system of claim 12, whereinthe processor is further configured to: receive computed tomography (CT)data associated with the patient's anatomy; and generate the virtualmodel associated with the patient's anatomy based on the CT data. 20.The computer-assisted surgery system of claim 12, wherein the virtualboundary is a virtual haptic boundary.